The present invention relates to metal casting apparatus and particularly to the portion of such apparatus and the method for positioning side mold segments in a first position to form a closed mold cavity and in a second position facilitating separation of a top core mold segment and a bottom core mold segment to release the cast article from the mold. The field of the invention particularly includes machines and apparatus for casting of vehicle wheels formed by gravity or pressure feeding molten metal into a multi-piece wheel mold that defines the mold cavity.
The present invention involves a form of metal casting particularly useful for casting vehicle wheels but also adaptable for use in casting other products particularly those with a predominantly circular cross-section. In a common form of such apparatus a multi-piece wheel mold consists of the following parts:
A face core which defines the outward face of the wheel, which one sees when the wheel is in an installed position; a top core which defines the inboard or brake side of the wheel; and the side cores (side mold segments), three or more in number which define what is commonly referred to as the rim of the wheel.
A typical mold contains one each top core and bottom core and four, five or six side cores. Each of these side cores are mounted in a core box which positions, moves and locks each side core in place by means of hydraulic or other actuators controlled by an electronic control system. In conventional casting apparatus known and used prior to the present invention, there was an extensive mass of apparatus used to position, slideably move and lock in place the side cores which form the rim portion of an automotive wheel. Such conventional casting apparatus to which the present invention is an improvement includes wheel casting machines using pressure feeding manufactured by Empire Castings Corporation (and disclosed at www.empirecastings.com). For known conventional wheel casting machines, one may also note U.S. Pat. No. 5,896,912 to Monroe, et al., entitled Method and Apparatus for Casting of Vehicle Wheel in a Pressurized Mold issued Apr. 27, 1999. The disclosures of the Monroe, et al. patent and the Empire Casting apparatus are incorporated by reference herein as an example of an apparatus and method known in the art to which the present invention is an improvement.
Prior apparatus for casting vehicle wheels and the like as discussed above have often employed massive and bulky core boxes for slideably moving and locking side cores in place, this makes it inherently difficult to facilitate and control the cooling of the portion of the side cores, particularly those that are in contact with the molten metal in the casting process. The massive, bulky core box structure also requires a larger overall casting apparatus with wider spaced columns for supporting and guiding the movable head which raises and lowers the top core mold apparatus. Furthermore, the core box arrangement in use prior to the present invention is deficient in accurately restraining and locking the side core molds relative to the top core mold and the bottom core mold thereby increasing a likelihood of unacceptable eccentricity in the vehicle wheel. Clearly, the highest degree of concentricity in a wheel casting is of utmost importance.
The present invention departs from the teaching of prior art apparatus and methods for casting of vehicle wheels primarily by providing improved apparatus and method for placing and displacing the multiple side mold segments forming a part of the mold cavity whereby a mold of greater integrity and accuracy of formation is achieved while at the same time reducing the bulk of the structure. Accordingly, the improved apparatus of the invention facilitates cooling by controlling uniform thickness of the mold sidewall while also eliminating the large bulk and mass of the prior art core box structure. Elimination of the core box structure with horizontal linear actuators makes it possible to reduce the overall size of the metal casting apparatus unit because the overall wheel casting unit size has been determined primarily to accommodate such core box structures. Metal casting apparatus for vehicle wheels or the like incorporating the present invention are generally similar to prior apparatus in that they include a bottom core or face core mold segment adapted to be affixed to a stationary bed of the casting apparatus and a top core mold segment adapted to be affixed to a vertically movable head of the casting apparatus. Rather than employing the conventional core box structures to move the multiple side mold segments (typically four in number) horizontally inward for closing the mold cavity and horizontally outward for opening the mold, a novel pivotally mounted side mold positioning and locking arrangement of minimal bulk and mass is provided by the present invention.
The side mold segments are each connected by a linkage to the movable head to cause them to move vertically upwardly and downwardly with the movable head while permitting independent lateral movement, typically arcuate movement about a pivot axis at or above the level of the top core mold segment. Actuators for each of the side mold segments are controlled to move each of the segments inwardly or outwardly to close or open the mold. Such actuators may typically be in the form of hydraulic cylinders pivotally connected at the cylinder connecting head to the movable head of the casting apparatus and having the cylinder pull-arm connected for producing pivotal motion of the side mold between a mold closing and a mold opening position. Other forms such as electromechanical or pneumatic actuators could alternatively be employed. In the preferred example described herein, it is advantageous to provide a latching mechanism for retaining the side cores in closed position in the form of a locator ring which engages arcuate tabs on the bottom of the side cores as the top core and side cores reach their limit of movement to seat on and seal with the bottom core. This gives great structural integrity to the mold assembly and assures great accuracy in positioning of the side cores which is important for maximizing concentricity of the wheel casting.
Among the objects and advantages of the present improved metal casting apparatus for vehicle wheels and other articles are the following:
The apparatus eliminates the present core box apparatus that horizontally moves and locks the side cores which is replaced by much less bulky structure, and eliminates former high repair and maintenance costs for this apparatus.
The apparatus frees up space in the lower area of the casting machine, allowing for redesign of smaller, potentially more economical casting machines to produce castings.
The apparatus provides for greater accessibility to all mold components during operation.
The improved apparatus eliminates prior mechanism to break side cores free from the outside rim area of the casting.
The side cores employed with the apparatus are of less complexity and hence their cost is reduced.
Initial mold cost for the apparatus is reduced by eliminating interlocks between the top core and face core and reducing the maintenance costs for those interlocks.
The apparatus provides significantly improved overall core concentricity, which will in turn improve the finished product and allow for less finishing stock on the casting, thereby providing advantages in material costs and processing costs.
The elimination of the prior core box horizontal positioning apparatus will significantly enhance the ability to further automate the simplified casting operation.
The apparatus according to the invention allows more freedom in mold wall design, particularly thickness and uniformity, and it allows more efficient cooling. This enhances the ability to promote controlled progressive solidification of the wheel. This will result in the formation of relatively smaller sized grains in the crystalline structure of the castings and improvement in the dendritic arm spacing of the finished product. This will in turn promote enhanced fatigue performance in the product and allow for the design of a more structurally efficient product.
In summary, this invention relates to an improved wheel casting apparatus, which will allow for significant saving in both material and process costs during the casting of a wheel. In addition, it will allow for enhanced controlling of the cooling process of the molten metal, forming a wheel superior in performance characteristics to wheels produced using the prior art. Faster and more controlled cooling results in an improved wheel casting having a finer grain size, increased strength, and reduced porosity. This turn will allow a reduction in finished product weight and in the material initially required to cast the wheel. Faster cooling will also allow for higher production rate. The invention""s features, at least in part, are adapted for use in providing improvements to casting apparatus for metal articles other than wheels.
In addition to the features and advantages of the improved metal casting apparatus according to the invention described above, further advantages thereof will be apparent from the following description in conjunction with the appended drawings.